This invention relates generally to pumps, and more particularly to pumps which work totally submerged in the pumped medium, which medium may contain a large amount of solid bodies. Pumps of this kind may be used as drainage pumps and pumps for sewage water.
When pumping such media, it has been shown that the so-called Vortex impeller pumps have many advantages, especially over pumps of relatively small dimensions.
A Vortex impeller pump, unlike a conventional centrifugal pump, has its impeller arranged beside the main medium current. This means that the pumped medium never passes through the impeller. The pump effect is obtained by the whirls that the impeller generates in the medium current.
Therefore, the risk of stopping decreases considerably. This approach allows pumps of small dimensions to be used for pumping such media.
These types of pumps, however, possess a special quality which can be very disadvantageous. The efficiency will, for natural reasons, be somewhat lower at moderate media currents, compared with that of a conventional centrifugal pump. By increasing media currents, the difference in efficiency increases and at the same time the head of the Vortex impeller pump decreases considerably. When using Vortex impeller pumps it has been impossible to limit the volume current which means that the head has often been too low. Further, operating costs have been high.